A surprisingly obscure fact is that all Piapro characters are licensed under the Creative Commons Attribution Non-Commercial 3.0 Unported license. I've found surprisingly few mentions of this on the internet. And furthermore, the few that do often have misconceptions.

One misconception is that the original artwork is under the CC-BY-NC 3.0 but the character design is not. This is obviously untrue if you do a little bit of thinking. If this were the case, the original image would be a derivative work of the character design and distribution would require meeting the licenses of both. So in effect, it would be no different than any random artist releasing their derivative work of a Piapro character into whatever free or not free license they choose.

The second misconception is that they are under a modified version of the CC-BY-NC that imposes additional restrictions. I think this misconception arises from Q11 on this FAQ (https://piapro.net/intl/en_for_creators.html): "When you copy or modify the Characters, please do not distort, mutilate, modify or take other derogatory action in relation to the Characters that would be prejudicial to Crypton's honor or reputation (please see Section 4e. of the full license). Some examples of prohibited uses include use in an overly violent context or in a sexual context."

However this misconception is not true. They are licensed under the original CC-BY-NC 3.0 Unported with no additional terms. The clause cited here is part of the original Creative Commons 3.0 licenses (including the not non-commercial ones) and was not added.

What this clause actually describes (rather unclearly) is moral rights. Depending on jurisdiction, moral rights may work differently from copyright, or even may even classified entirely separately. In some jurisdictions, moral rights can last indefinitely. So, in those jurisdictions, even works that would be otherwise in the public domain could in theory still be affected by moral rights.

All Creative Commons licenses do not waive or affect moral rights <https://creativecommons.org/2007/11/07/cc-oa-moral-rights/> - not even the CC0. There is one exception, which is that they stipulate that those rights shall be agreed to be waived by their holder in jurisdictions where enforcement of moral rights would compromise the ability to make derivative works, and where waiving the rights is possible. This is actually what the purpose of that clause is, it was just worded rather unintuitively in the 3.0 licenses so that it seemed to sound like it imposed additional restrictions on the estate copyright (however it does not actually do that <https://law.stackexchange.com/questions/103149/do-creative-commons-licenses-forbid-immoral-use>).

Later versions of the license improved the wording <https://wiki.creativecommons.org/wiki/4.0/Moral_rights> as to not make it sound like it imposed additional restrictions, however the legal meaning remained identical. In many jurisdictions (notably USA; to the point where many scholars debate if the USA is even following the Berne convention <https://www.copyrightlaws.com/moral-rights-in-u-s-copyright-law/>), moral rights are barely existent to the point where they aren't enforced except in the most extreme cases, which would often be covered by other laws such as defamation anyway. In others, such as Japan and Canada, moral rights are so strict that the non-enforcement clause comes into play. So really, this clause actually serve to increase freedom to the user, rather than restrict it.

As for why the Crypton FAQ - which is not a legal document, and even if it was, would not matter as the work has been irrevocably released under the CC-BY-NC 3.0 Unported) - says that; I'm not sure. One possible explanation is that it was based on a Japanese document which referenced the Piapro Character License (which DOES actually include a clause forbidding some uses), and the translator (who was presumably not a lawyer) was told that the CC-BY-NC was the "international license" as opposed to PCL (which they sometimes describe as being designed for Japanese law only), and just skimmed the text of the CC-BY-NC looking for what they assumed to be the closest match to the PCL clause.

Another explanation is just that it is just a suggestion/guideline and not stated to be a part of the license. The use of the informal words "rule" and "please" may be imply this.